Controlled bridges may permit to enable a load when an event occurs and to implement a soft-start process by controlling the inrush current.
Controlled bridges may be implemented in a number of ways such as, e.g.: electromechanical solutions using relays, electronic solutions using silicon-controlled rectifiers—e.g. SCRs.
Electromechanical solutions may use a relay to implement both event load enabling and soft-start.
For instance, in such a solution load enabling may be achieved by driving a first switch having cascaded a parallel connection of a second switch and a resistor to implement the inrush current control. The resistor may limit the current that tends to flow into a capacitor while charged. Such a capacitor may have a high capacitance value and the inrush current would tend to have a high value as well. Once the capacitor is well charged the resistor is no longer useful and may be shorted by the second switch to avoid power losses that would adversely affect efficiency. An auxiliary power supply (e.g. a SMPS) and a micro controller unit (MCU) may be required in order to drive the two switches.
While offering some advantages (e.g. galvanic isolation), such a solution may exhibit various drawbacks, e.g.: high cost (relays used as switches and sense resistors may be expensive), poor reliability (relay operation lifetime and reliability may be low in comparison with electronic devices), risk of undesired relay opening due to e.g. vibrations, explosion hazard in flammable environment, acoustic noise, and high current consumption to drive the relay coil.
Other than for those cases where galvanic isolation is an asset, these drawbacks may suggest to refer to electronic solutions e.g. including SCRs.
These solutions may still exhibit certain drawbacks such as e.g.: increased design complexity and cost due e.g. to the possible use of a floating supply, if a floating supply is not used, dedicated opto- or magnetic couplers for the SCR control may be used, which however has an impact on the overall cost. Further, these solutions may not be friendly in terms of back-compatibility (e.g. as these may involve redesigning magnetics for existing designs not intended to be controlled).
There is a need in the art to provide an improved solution dispensing with at least some, and notionally all, of the drawbacks outlined in the foregoing.